In Part 3 of this series we will install NexentaStor, make some file systems and discuss the advantages and disadvantages of NFS and iSCSI as the storage backing. By the end of this segment, we will have everything in place for the ESX and ESXi virtual machines we’ll build in the next segment.

Part 3, Building the VSA

For DRAM memory, our lab system has 24GB of RAM which we will apportion as follows: 2GB overhead to host, 4GB to NexentaStor, 8GB to ESXi, and 8GB to ESX. This leaves 2GB that can be used to support a vCenter installation at the host level.

Our lab mule was configured with 2x250GB SATA II drives which have roughly 230GB each of VMFS partitioned storage. Subtracting 10% for overhead, the sum of our virtual disks will be limited to 415GB. Because of our relative size restrictions, we will try to maximize available storage while limiting our liability in case of disk failure. Therefore, we’ll plan to put the ESXi server on drive “A” and the ESX server on drive “B” with the virtual disks of the VSA split across both “A” and “B” disks.

Our VSA Virtual Hardware

For lab use, a VSA with 4GB RAM and 1 vCPU will suffice. Additional vCPU’s will only serve to limit CPU scheduling for our virtual ESX/ESXi servers, so we’ll leave it at the minimum. Since we’re splitting storage roughly equally across the disks, we note that an additional 4GB was taken-up on disk “A” during the installation of ESXi, therefore we’ll place the VSA’s definition and “boot” disk on disk “B” – otherwise, we’ll interleave disk slices equally across both disks.

Datastore – vLocalStor02B, 8GB vdisk size, thin provisioned, SCSI 0:0

Guest Operating System – Solaris, Sun Solaris 10 (64-bit)

Resource Allocation

CPU Shares – Normal, no reservation

Memory Shares – Normal, 4096MB reservation

No floppy disk

CD-ROM disk – mapped to ISO image of NexentaStor 2.1 EVAL, connect at power on enabled

Network Adapters – Three total

One to “VLAN1 Mgt NAT” and

Two to “VLAN2000 vSAN”

Additional Hard Disks – 6 total

vLocalStor02A, 80GB vdisk, thick, SCSI 1:0, independent, persistent

vLocalStor02B, 80GB vdisk, thick, SCSI 2:0, independent, persistent

vLocalStor02A, 65GB vdisk, thick, SCSI 1:1, independent, persistent

vLocalStor02B, 65GB vdisk, thick, SCSI 2:1, independent, persistent

vLocalStor02A, 65GB vdisk, thick, SCSI 1:2, independent, persistent

vLocalStor02B, 65GB vdisk, thick, SCSI 2:2, independent, persistent

NOTE:It is important to realize here that the virtual disks above could have been provided by vmdk’s on the same disk, vmdk’s spread out across multiple disks or provided by RDM’s mapped to raw SCSI drives. If your lab chassis has multiple hot-swap bays or even just generous internal storage, you might want to try providing NexentaStor with RDM’s or 1-vmdk-per-disk vmdk’s for performance testing or “near” production use. CPU, memory and storage are the basic elements of virtualization and there is no reason that storage must be the bottleneck. For instance, this environment is GREAT for testing SSD applications on a resource limited budget.

In Part 1 of this series we introduced the basic Lab-in-a-Box platform and outlined how it would be used to provide the three major components of a vMotion lab: (1) shared storage, (2) high speed network and (3) multiple ESX hosts. If you have followed along in your lab, you should now have an operating VMware ESXi 4 system with at least two drives and a properly configured network stack.

In Part 2 of this series we’re going to deploy a Virtual Storage Appliance (VSA) based on an open storage platform which uses Sun’s Zetabyte File System (ZFS) as its underpinnings. We’ve been working with Nexenta’s NexentaStor SAN operating system for some time now and will use it – with its web-based volume management – instead of deploying OpenSolaris and creating storage manually.

Part 2, Choosing a Virtual Storage Architecture

To get started on the VSA, we want to identify some key features and concepts that caused us to choose NexentaStor over a myriad of other options. These are:

NexentaStor is based on open storage concepts and licensing;

NexentaStor comes in a “free” developer’s version with 4TB 2TB of managed storage;

While the performance features of NexentaStor/ZFS are well outside the capabilities of an inexpensive “all-in-one-box” lab, the concepts behind them are important enough to touch on briefly. Once understood, the concepts behind ZFS make it a compelling architecture to use with virtualized workloads. Eric Sproul has a short slide deck on ZFS that’s worth reviewing.

ZFS and Cache – DRAM, Disks and SSD’s

Legacy SAN architectures are typically split into two elements: cache and disks. While not always monolithic, the cache in legacy storage typically are single-purpose pools set aside to hold frequently accessed blocks of storage – allowing this information to be read/written from/to RAM instead of disk. Such caches are generally very expensive to expand (when possible) and may only accomodate one specific cache function (i.e. read or write, not both). Storage vendors employ many strategies to “predict” what information should stay in cache and how to manage it to effectively improve overall storage throughput.

New cache model used by ZFS allows main memory and fast SSDs to be used as read cache and write cache, reducing the need for large DRAM cache facilities.

Samsung's new SSD generation using multi-level cell (MLC) flash and a multi-channel flash controller with NCQ and 128MB SDRAM cache.

Tom’s Hardware has a good review on the state of current SSD options out there. As discussed in previous posts, the ZFS file system offers hybrid storage aspects out of the box. This game-changing technology allows for “holy grail” levels of price-performance with the key technology being SSD for caching. That’s the value proposition our friends at Nexenta have been preaching.

To see what this means in a ZFS storage environment, go no farther than Sun’s blog: Brendan Gregg has posted a great blog on how ZFS’ L2ARC can be comitted to SSD to dramatically increase effective IOPS and drastically reduce latency. The results speak for themselves…

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